The invention relates to a contour collimator for radiation therapy having a plurality of diaphragm elements arranged movably with respect to each other, such movement being powered by a drive unit.
A contour collimator of this kind is known for example from DE 195 36 804.5 A1. In the contour collimator described therein, a drive unit is provided for each of the plurality of diaphragm elements, and the drive units move the diaphragm elements in two directions along a guide rail. By means of the control for each individual diaphragm element, a radiation field is set up with which it is possible to create a special contour for radiation on the body part that is being radiated. This contour collimator is especially suitable for small radiation fields. It is impossible to increase the size of this known contour collimator in order to create larger radiation fields because the motors such an increase in size would necessitate are too big and they can scarcely be arranged about the radiation field.
The task of the present invention was therefore to adapt a known contour collimator in such a way that it is also suited for use with larger radiation fields.
This task has been solved by supporting the diaphragm elements only on the side of the drive unit.
The invention is based on the premise that the diaphragm elements must be both supported and movable. In the known contour collimator, this facility is provided in the form of a rail that supports the weight of the diaphragm elements and guides them in courses parallel to one another.
However, particularly when larger diaphragm elements are used, a high degree of friction is generated in the guide rails, the diaphragm elements tend to jam, and they cannot be moved without the application of much power. The use of larger motors leads to increased size of the contour collimator, an undesirable and unacceptable increase in weight and, most importantly, to space problems since the motors should be arranged as closely as possible to the diaphragm elements.
However, the diaphragm elements of the contour collimator according to the invention are preferably only supported in the area of the drive unit by means of a fixed bearing. The additional guides that are necessary for the diaphragm elements are for positioning purposes only and do not support any of the elements"" weight. Jamming is prevented by the proximity of the support to the drive unit, and lower forces are required to move the diaphragm elements. Consequently, the motors can be smaller and can be arranged beside one another in very limited space.
One particularly advantageous embodiment provides for a toothed rack on the diaphragm elements in the area of the drive unit. This toothed rack allows, for example, allows it to operate in conjunction with a gearwheel driven perpendicularly to the direction of movement of the diaphragms, thus achieving a transmission of power with minimal loss. The toothed rack also contributes to a highly compact construction of the contour collimator, since it allows the drive units to be arranged very closely together.
It is further advantageous if a guide for the diaphragm elements is also arranged in direct proximity to the drive unit. The guide in the area of the drive unit ensures reliable cooperation between drive unit and diaphragm element, and particularly when toothed rack and gearwheel cooperate, the guide ensures that the elements remain securely positioned relative to each other.
In order to ensure that the movement of the diaphragm elements generates as little friction as possible, it is proposed to provide a loose bedding for the diaphragm elements on the side of the elements that faces the drive unit. This loose bedding absorbs only minimal lateral weight in a plane perpendicular to the direction of movement of the diaphragms and its primary function is to ensure that the diaphragm elements are guided essentially parallel to each other.
In a preferred configuration, at least two diaphragm elements are arranged with some separation, opposite and slightly offset relative one another, and movably towards one another in more than half the distance of separation. This arrangement provides the capability of xe2x80x9cover travelxe2x80x9d, which allows the formation of special contours and the interlacing of oppositely arranged diaphragm elements.
In order to adjust the contour collimator optimally to the beam path of the radiation beam, it is proposed that the longitudinal axes of at least two diaphragm elements form an angle in their extent from the drive units to their facing sides. In this way, the diaphragm elements can be constructed conically and arranged in a fan formation, with the fan broadening in the direction of the beams being used.
It is advantageous if at least two diaphragm elements have the same length in their extent from the drive units to their facing sites. Indeed, all diaphragm elements preferably have essentially the same shape, in order to reduce the costs of manufacturing the diaphragm elements and to facilitate replacement of faulty diaphragm elements.
A significant reduction in the weight of the diaphragm elements can be achieved if the side of the diaphragm element in the area of the drive units in the direction of movement of the diaphragm elements is longer than its opposite side. Whereas the drive unit cooperates with the diaphragm element on its longer side, the diaphragm element only reaches its full height in the area in which it comes into contact with the radiation.
The collimator can be adjusted rapidly to the most varied operating requirements if at least two and preferably half of the diaphragm elements form a diaphragm group, which is disposed movably in the direction of movement of the diaphragm elements in addition to the movement of the individual diaphragm elements. In this way, the diaphragm group can be simply displaced as a whole, thereby enabling the radiation field to be rapidly enlarged or reduced.
This is preferably achieved by arranging two diaphragm groups opposite one another in the direction of movement of the diaphragms and movably towards one another on guide rails. For example, the contour collimator can then be operated with a high degree of overtravel with closely adjacent diaphragm groups. On the other hand, diaphragm groups having a large separation distance allow the formation of a particularly large and contoured radiated area.
A highly compact configuration of the contour collimator can be achieved if the drive unit is equipped with an axle disposed perpendicularly to the diaphragm element and connected to a motor. In this way, it is possible to provide many closely arranged motors to drive many diaphragm elements. Not only does this result in a particularly compact configuration, but the closely arranged motors can also be controlled easily, and are easily replaced in case of damage.
The design according to the invention particularly allows one drive unit to be assigned to each diaphragm element, so that it is possible to configure the position of the diaphragm elements on an individual basis.
In order to transfer the position of the diaphragm elements to a data processing system for purposes of monitoring and documentation, it is proposed that each drive unit be equipped with a rotary potentiometer, attached with minimal space requirement, or with a linear potentiometer arranged parallel to the diaphragm elements, or with other measuring systems such as inductive or optical systems.